Dengue outbreaks have been reported in communities along the
Mexico--US border since 1980 (1); however, during
1987--July 1999, no cases were reported from Laredo, Texas (1999 population: 162,000). During
January--July 1999, approximately 300--325 dengue cases were reported from Nuevo
Laredo, Tamaulipas, Mexico (1999 population: 274,000), a city across the Rio Grande
from Laredo. To determine whether undiagnosed or unreported dengue cases had
occurred in Laredo, the Texas Department of Health (TDH) reviewed medical records from
five Laredo health facilities (the two city hospitals and the three largest of five
community clinics). This report summarizes the findings of the review, which indicated that
during July 23--August 20, 1999, 50% of suspected case-patients had undiagnosed
dengue infection. Recognition of the diagnosis of dengue can be improved through
heightened surveillance, professional and public education, and prompt reporting of cases by
the health-care providers to local or state health departments.
Medical records were reviewed for all patients who presented to one of the
five facilities with fever, arthralgias, myalgias, rash, or headache during July
23--August 20. A case of dengue was suspected in a person aged
>5 years with a temperature of
>101 F (>38.3 C) and rash of any duration or fever for
>3 days without cough or diarrhea. During August
20--October 31, blood was drawn from suspected
dengue case-patients and serum samples were tested for antidengue IgG and dengue
IgM antibodies at the TDH laboratory. A confirmed case of recent dengue was defined as
a positive IgM test or a fourfold or greater increase in the IgG antibody titer
between acute- and convalescent-phase serum samples.
Forty-nine suspected dengue case-patients were identified from 494 records;
24 (49%) were located and interviewed. Of these, 22 (92%) agreed to provide a
serum sample. Eleven case-patients had serologic evidence of recent dengue infection;
10 (91%) of the 11 tested positive for both IgM and IgG antibodies. One case-patient
was negative for IgM antibodies but had a fourfold increase in IgG antibody titers over a
3-month period. Symptoms reported by the 11 confirmed case-patients included
fever (100%), arthralgias (73%), headache (64%), malaise (64%), and rash (45%).
Discharge diagnoses of "viral syndrome" or "viral fever" were given to nine (82%) and
"flu-like illness" were given to two (18%). Nine case-patients reported a history of travel
to Mexico within 2 weeks of illness onset; two had not been outside Texas.
Reported by: G Peña, City of Laredo Health Dept, Laredo; E Svenkerud, MD, Bur
of Communicable Disease Control; B Liszka, Bur of Laboratories; K Hendricks, MD, J
Rawlings, MPH, Infectious Diseases Epidemiology and Surveillance Div, Texas Dept of Health. Div
of Applied Public Health Training, Epidemiology Program Office; Dengue Br, Div
of Vectorborne Infectious Diseases, National Center for Infectious Diseases; and an EIS
Dengue is an arboviral illness of tropical and subtropical
areas commonly transmitted by Aedes aegypti mosquitoes
(2,3). Approximately 2.5 billion persons live in regions where dengue is endemic and
50--100 million infections occur
annually (2,4). Although infection may result in lifelong homotypic immunity,
cross-protective immunity does not occur among the four dengue virus serotypes.
Infection with any dengue serotype can be asymptomatic or can cause dengue,
dengue hemorrhagic fever (DHF), or dengue shock syndrome (DSS). DHF and DSS are
life-threatening conditions (5). Since the 1970s, outbreaks of dengue, DHF, and DSS
have increased in frequency and severity in the Americas and the Caribbean
Dengue may present as an undifferentiated febrile illness and unless
physicians retain a high level of suspicion, a dengue diagnosis may be missed easily in
areas where the virus is not endemic. Laboratory testing is necessary for
diagnostic confirmation. Acute- and convalescent-phase serum samples should be obtained
for diagnosis and sent for confirmation to state or territorial health
department laboratories. Serum samples should be accompanied by a summary of clinical
and epidemiologic information, including onset date, sample collection date, and a
travel history for the 3 weeks before illness onset.
An estimated two million crossings occur each month between Laredo and
Nuevo Laredo, and Ae. aegypti is found in both cities. Movement of infected persons
can introduce the virus into dengue-free areas. Travelers to regions where dengue
is endemic should avoid exposure to mosquito bites by using repellents and
protective clothing and by staying in well-screened or air-conditioned quarters. Residents
of areas where dengue is endemic and Mexico-US border communities can reduce
the Ae. aegypti population in and around homes by changing water in bird baths or
flower vases daily, tightly covering stored water receptacles, and eliminating old
tires, containers, tree holes, and other potential mosquito breeding sites.
Following identification of dengue cases, the Laredo Health
Department implemented mosquito reduction activities (e.g., aggressive refuse and tire
disposal campaigns and insecticide fogging). Dengue alerts were sent to health-care
providers, and mosquito reduction and personal protection information was distributed
through health fairs and schools. Information exchange increased substantially between
health officials from Laredo and Nuevo Laredo. Although no suspected cases were
reported before the alerts were issued, 161 suspected dengue cases were reported during
mid-August--December 1999; 18 cases tested positive for dengue. No positive cases
were reported from Laredo in 2000.
When a case of dengue is confirmed in a community, the public health
response should include education of health-care providers and the public,
intensified surveillance, and enhanced vector-control activities. Additional information
about dengue is available on the World-Wide Web, http://www.cdc.gov/ncidod/dvbid/dengue.htm.
- Rawlings JA, Hendricks KA, Burgess CR, et al. Dengue surveillance in Texas, 1995. Am
J Trop Med Hyg 1998;59:95--9.
- Gubler JG. Dengue and dengue hemorrhagic fever: its history and resurgence as a
global public health problem. In: Gubler DJ, Kuno G, eds. Dengue and dengue hemorrhagic
fever. New York, New York: Cab International,
- Pan American Health Organization. Dengue and dengue hemorrhagic fever in the
Americas: guidelines for prevention and control. Washington, DC: Pan American Health
Organization, 1994 (Scientific publication no. 548).
- Halstead SB. Pathogenesis of dengue: challenges to molecular biology.
- Henchal EA, Putnak JR. Dengue viruses. Clin Microbiol Rev
- Pan American Health Organization. Reemergence of dengue in the Americas.
Epidemiological Bulletin of the Pan American Health Organization